Duplex chain conveyors are classified either as a so-called truck conveyor wherein the article carrier is a truck which moves on a floor and has trolley devices thereon, and a free rail for guiding the movement of a trolley device is laid in the floor, or as a so-called overhead conveyor wherein a trolley device moves within an overhead free rail and from the trolley device there depends a hanger as the article carrier.
Heretofore, there have been a duplex chain conveyors of the type disclosed in Japanese patent Publication No. 38391/1972 wherein a pusher dog and a retainer which are brought into engagement and disengagement with respect to a pusher are pivoted for rise and fall motion to a trolley device, and a duplex chain conveyor of the type disclosed in Japanese patent Publication No. 15272/1978 wherein a pusher and a retainer are pivoted for rise and fall motion to a driving chain. In both types, however, the pusher or the pusher dog and the retainer are pivotally supported separately from each other. Particularly, the pusher and the retainer shown in the latter patent publication are provided with an interlocking mechanism using links whereby both can rise or fall simultaneously, and the provision of such an interlocking mechanism results in a more complicated structure of the entire device. Besides, since the engaging/disengaging mechanism for the pusher or the pusher dog and the hook is positioned between a power rail and a free rail, it is impossible to perform the engaging and disengaging operation from outside the power rail or free rail, and it is difficult to confirm the state of engagement or disengagement.